The subject matter of the present application is related to remotely operated electrical switching apparatus. Specifically, new apparatus is described which permits remote switching of a common load into and out of a circuit from multiple locations.
In the past, it has been found useful to arrange lighting circuits, and other electrical loads, to permit the energization of the light from different locations. In installations such as these, first and second switches are located away from the light to be activated. A common relay is connected to each of the switches, the relay being of the latching type. With suitable circuitry interconnecting the light load, a source of power, and the individual control switches, it is possible to activate and deactivate the lighting load from multiple locations.
FIG. 1 is illustrative of one such prior art switching circuit. A latching type relay 12 is energized from a source of electrical voltage 10 when current path 17, 18 or 19 is conductive. Each of the current paths comprises a switch 20 operatively connecting the common side of a power source 10 through one of the back-to-back diodes 27 and 28 to a winding 12a of the latching type relay. The latching type relay is equipped with an auxiliary set of fixed contacts 12b and 12c which are alternately connected to the movable contact 12b. The circuit path is completed through back-to-back diodes 14 and 15 to the remaining side of the electrical power source 10.
Thus, with the movable contact 12d in the position shown, load 11 remains unenergized. Closure of switch 20 to fixed contact 20a permits current to flow through diode 27 thereby energizing relay winding 12a. The energization of relay winding 12a will close main contacts 12e and place movable contact 12d into contact with fixed contact 12b. At this time, diode 14, because of its polarity, inhibits further current from energizing relay 12a.
As FIG. 2 indicates, relay 12 is equipped with a permanent magnet 12h which will hold the movable contact in position until a subsequent current is supplied to winding 12a in a direction opposite from that previously supplied.
Referring once again to FIG. 1, it is clear that the operation of any of the switches in current path 17, 18, and 19 to connect diode 28 to the one side of power source 10 will permit current flow in the proper sense for opening contacts 12e and moving movable contact 12d back into connection with fixed contact 12c. Light emitting diodes 23, 25, hereinafter LED 23, 25, indicate the present position of movable contact 12d. The LED 23, or 25, which is of the same polarity as the diodes 14 or 15 presently in contact with movable contact 12d, will be illuminated indicating the state of relay 12.
The difficulty with using apparatus in accordance with FIGS. 1 and 2, is that a simultaneous closure of current path 17 or 18, by operating at the same time a switch located in either of these current paths, will cause multiple changes in the state of relay 12. The associated relay contact bounce provides for arcing on the main contacts 12e which reduces the life of the relay 12. Further, this operation will cause a rapid movement in the armature of the relay 12 generating objectionable noise as well as burning the main contacts 12e.
A further example of the prior art is shown in FIGS. 3 and 4. Both of these prior art devices employ the use of a capacitor 30, and 32. In the device of FIG. 3, the auxiliary contacts of the magnetic relay 12 are not used. With capacitor 30, the closure of switch 20 to one of the available contacts will permit current to charge capacitor 30. During the charging interval, sufficient current enters relay winding 12a to permit the relay to change state. When the load 11 is to be switched again, one of the switches 20 is moved to the opposite contact thereby permitting current of an opposite sense to be supplied to capacitor 30 charging the capacitor in an opposite sense. During this time sufficient current flows through winding 12a to permit energization of the relay thereby changing the state of contacts 12e.
With the prior art device of FIG. 4, the auxiliary contacts are used with the magnetic relay. Capacitor 32 is charged through resistor 31 to a voltage having a polarity dependent upon the position of movable arm 12d of the auxiliary contacts. In the position shown in FIG. 4, capacitor 32 receives a current from diode 14 thereby establishing the shown voltage polarity. If either switch 33 or 34 is closed, the capacitor 32 voltage discharges through the winding 12a permitting the relay armature to be moved from its previous position which will move movable contact 12d into contact with fixed contact 12c. At this time, the reverse voltage polarity is established on capacitor 32 which, upon subsequent activation of switches 33 or 34, will supply current in an opposite direction through winding 12a changing the state of the relay contacts.
These examples of the prior art have similar problems when operating switches are continuously actuated at separate locations. The charging and discharging of the capacitors causes an unstable movement in the magnetic latching relay armature. The movement is responsible for arcing and possible fusion of the main contacts 12e. Further, there is the problem in the embodiment shown in FIG. 4 that the capacitor can be insufficiently charged when switches are simultaneously activated.